The present invention relates to a method of manufacturing a semiconductor device and, more particularly, to a method of forming a hardmask pattern in which the pitch of a pattern is less than the resolution of the exposure equipment used.
The smallest pitch of a pattern formed in a photolithography process is varied depending on the wavelength of exposure light used in the exposure equipment. As the level of integration of semiconductor devices is accelerated, light with a wavelength shorter than what is being used now must be used to decrease the pitch of the pattern. To this end, X-ray or e-beam may be used, but this is still in the experimental stage due to technical problems, productivity, and so on. Accordingly, a Double Exposure and Etch Technology (DEET) has been proposed.
FIGS. 1A to 1C are views illustrating a conventional double exposure etch technique.
Referring to FIG. 1A, a first photoresist PR1 is coated over an etch target layer 11 and a semiconductor substrate 10. After the first photoresist PR1 is patterned by exposure and development processes, the etch target layer 11 is etched using the patterned first photoresist PR1 as a mask. At this point, the etched etch target layer 11 has a line width of 150 nm and a space width of 50 nm.
The first photoresist PR1 is removed. A second photoresist PR2 is coated over the entire surface. As illustrated in FIG. 1B, the second photoresist PR2 is patterned by exposure and development processes so that parts of the etch target layer 11 is exposed.
The etch target layer 11 is etched again by using the patterned second photoresist PR2 as a mask, thus forming a pattern having a line and space width of 50 nm, as illustrated in FIG. 1C. The second photoresist PR2 is then removed.
In the DEET, overlay accuracy during the exposure process of the second photoresist PR2 is directly connected to a Critical Dimension (CD) variation of the final pattern. In reality, overlay accuracy of the exposure equipment is difficult to control below 10 nm, thus making it difficult to decrease CD variation of the final pattern. Furthermore, there is a difficulty in controlling circuit separation through Optical Proximity Correction (OPC) over the double exposure.